Clot detection methods for clotting time testing

ABSTRACT

Aspects of the disclosure relate to clotting time tests detect clotting time based on the viscosity changes of a fluid sample, using a disk dropped within a test chamber containing the fluid sample from a disk maximal position to a disk minimal position, which is a point at which the disk settles within the fluid sample. Changes in the disk minimal position as multiple test cycles are conducted are used in assessing formation of a clot within the fluid sample. Methods of assessing such changes in the disk minimal position are disclosed.

TECHNICAL FIELD

The present disclosure relates to detecting changes in viscosity of biologic fluid test samples, e.g., detecting coagulation and coagulation-related activities including agglutination and fibrinolysis of human blood test samples, and more particularly to improved methods and apparatus for early detection of a clotting event in a blood test sample.

BACKGROUND

Blood coagulation is a complex chemical and physical reaction that occurs when blood comes into contact with an activating agent, such as an activating surface or other activating agent. In this context, the term “blood” means whole blood, citrated blood, platelet concentrate, plasma, or control mixtures of plasma and blood cells, unless otherwise specifically called out otherwise; the term particularly includes heparinized blood.

Several tests of coagulation are routinely utilized to assess the complicated cascade of events leading to blood clot formation and test for the presence of abnormalities or inhibitors of this process. Among these tests are activated clotting time (ACT), which includes high range ACT (HRACT), a test which features a slope response to moderate to high heparin levels (up to 6 U/mL) in whole blood drawn from a patient during cardiac surgery. The ACT test formulated to respond to low heparin levels (0.1 to 1.0 U/mL) in whole blood drawn from a patient during the extracorporeal membrane oxygenation (ECMO) procedure is low range ACT (LRACT).

Unfractionated heparin is most commonly used for anticoagulation during cardiac pulmonary bypass (CPB) surgery to prevent gross clotting of the bypass circuit and more activation and consumption of coagulation system components. While an ACT test responds to heparin, it is a global assessment of coagulation status of blood and affected by many other factors other than heparin, such as hemodilution and temperature. Due to the limitation of ACT monitoring and the variability of patient response to heparin dose, individualized heparin and protamine management based on heparin protamine titration test has associated with improved clinical outcomes. The heparin protamine titration test uses activated clotting time as test end point.

During heart bypass surgery, the platelets of blood circulated in an extracorporeal circuit may become activated by contact with the materials present in the extracorporeal circuit. This activation may be reversible or irreversible. Once platelets are irreversibly activated, they lose their ability to function further. A deficiency of functional platelets in the blood may be indicative of an increased probability of a post-operative bleeding problem. Such a deficiency, and the resulting post-operative bleeding risk, could be remedied by a transfusion of platelet concentrate. Platelet functionality tests, which can use activated clotting time as a test end point, can identify a deficiency of platelets or functional platelets and aid the attending surgeon in ascertaining when to administer a platelet concentrate transfusion. Such a test is further useful in ascertaining the efficacy of a platelet transfusion. By performing the platelet functionality test following a platelet transfusion, it is possible to determine if additional platelet concentrate transfusions are indicated. Real-time assessment of clotting function at the operative site may be performed to evaluate the result of therapeutic interventions and also to test and optimize, a priori, the treatment choice and dosage.

Other anticoagulant drugs used in cardiac surgery and cardiac catheterization procedures, such as low molecular weight heparin and bivalirudin, are also monitored with activated clotting time. The clotting time test used to monitor bivalirudin uses ecarin as activator, thus the test is called ecarin time (ECT).

ACT tests are based on the viscosity change of a test sample within a test chamber. During a test cycle, a ferromagnetic washer immersed in the test sample is lifted to the top of the test chamber by magnetic force produced by a magnetic field located at the top of the test chamber; the washer is then held at the top of the test chamber for a specific time. After the specified holding time, the washer is then dropped through the test sample via gravity. The increased viscosity due to the clotting of the test sample slows the motion of the washer. Thus, if the time that the washer travels through a specified distance (i.e., the washer “drop time”) is greater than a preset value (the clot detection sensitivity threshold), a clot is indicated to be detected and an ACT value is reported.

A particular apparatus and method for detecting changes in human blood viscosity based on this principle is disclosed in U.S. Pat. Nos. 5,629,209 and 6,613,286, in which heparinized blood is introduced into a test cartridge through an injection port and fills a blood receiving/dispensing reservoir. The blood then moves from the reservoir through at least one conduit into at least one blood-receiving chamber where it is subjected to a viscosity test. A freely movable ferromagnetic washer is also located within the blood-receiving chamber that is moved up using an electromagnet of the test apparatus and allowed to drop with the force of gravity. Changes in the viscosity of the blood that the ferromagnetic washer falls through are detected by determining the position of the ferromagnetic washer in the blood-receiving chamber in a given time, or by a given number of rises and falls of the ferromagnetic washer. Air in the conduit and blood-receiving chamber is vented to atmosphere through a further vent conduit and an air vent/fluid plug as the blood sample is fills the blood-receiving chamber.

The movement of the washer in the above approach is actively controlled only when it is moved up, and the washer passively drops with the force of gravity. Increased viscosity from blood clotting decreases the velocity of the washer drops in the test chamber. A drop time greater than a preset threshold value indicates clotting of the test sample. Blood samples which have high levels of heparin usually produce very weak clots that may easily be destroyed by the lifting movement of the washer. If the clot threshold is set low to detect the weak clots, however, false detections often occur during early testing cycles when activators are not fully suspended during the mixing cycle.

The present disclosure addresses problems and limitations associated with the related art.

SUMMARY

Aspects of the present disclosure relate to methods for detecting a blood clot in a fluid sample at an early clot formation stage based on a fluid viscosity change of the sample. Aspects of the disclosure can be used in clotting time tests to increase test sensitivity. Examples of Clotting Time tests in which aspects of the present disclosure are useful include, but are not limited to, Activated Clotting Time (ACT), Prothrombin Time (PT), Activated Partial Thromboplastin Time (APTT), and Ecarin Clotting Time (ECT).

The ACT test is one of the tests most widely used to monitor the effect of high level of heparin (up to 6 U/ml) in the sample during cardiac pulmonary bypass surgery. During a test cycle of the disclosed methods, a ferromagnetic disk is positioned at a Disk Maximum Position within a test chamber of a fluid viscosity testing device by magnetic force produced by the magnetic field. The disk is then held at the Disk Maximum Position for a specified time. After the specified holding time, the magnetic force is released so that the disk falls through the fluid sample due to the force of gravity to a Disk Minimum Position. Parameters relating to the disk movement indicative of a change in fluid viscosity can be measured with a position detector.

It is advantageous to detect clots in the fluid sample as quickly as possible. Therefore, the threshold(s) in which changes in the fluid sample are compared to identify a clot are often set low. Low change thresholds, however, can potentially result false detection of clots (i.e. erroneous test results) due to noises of sensors, disk positions, and reagent uniformity, for example. Therefore, any clot detection thresholds need to be at a value to avoid false detection. The present inventors have discovered that by evaluating a change in the Disk Minimum Position (i.e. the lowest point within the test chamber in which the disk falls during a test cycle) and/or integration of a Disk Minimum Position in a Disk Minimum Sum over a certain test period(s) as additional or sole clot detection end point or threshold, clot formation can be accurately detected at an early clot formation stage. It is believed that one advantage of evaluating changes in the Disk Minimal Position is that an increase in Disk Minimal Position or integration of Disk Minimal Position between test cycles is more reliably related to clot formation and less affected by potential noise introduced by position sensors and disk movement as compared other disclosed clot detection parameters assessed such as Disk Drop Span as a function of test time or Disk Drop Velocity as a function of test time.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages and features will be more readily understood from the following detailed description of various embodiments, when considered in conjunction with the drawings, in which like reference numerals indicate identical structures throughout the several views, and in which:

FIG. 1, which is based on FIG. 13 of U.S. Pat. No. 5,629,209, is a cross-sectional view of a cartridge positioned within a machine.

FIG. 2, which is based on FIG. 12d of U.S. Pat. No. 5,629,209, is a partial cross-sectional view of the cartridge of FIG. 1.

FIG. 3 is a schematic cross-section of the test chamber portion of the cartridge of FIGS. 1 and 2.

FIG. 4A is a flowchart of a first embodiment, a portion of which is shown in greater detail in FIG. 4B.

FIG. 5 is a flowchart of a second embodiment.

FIG. 6 is a schematic illustration of portions of the second embodiment.

FIG. 7 is a set of four graphs, one for each of four zones, showing zone counts and scale factors as a function of time.

FIG. 8 is a set of four graphs, one for each of four zones, showing another set of zone counts and scale factors as a function of time.

FIG. 9 is a schematic graph of the components of a Disk Cycle.

FIG. 10 is a schematic graph of the disk Distance Span over the Drop Portion of a Disk Cycle.

FIG. 11 is a schematic graph of parameters related to the Disk Drop Velocity.

FIG. 12 is a schematic graph of parameters related to the Disk Scale.

FIGS. 13 and 14 are schematic graphs of the Drop Velocity Calibration process in first and second passes, respectively.

FIG. 15 is a flowchart of a third embodiment.

FIGS. 16-18 are sets of paired graphs (two graphs in each figure), showing measurements of various results of testing of the third embodiment.

FIG. 19 is a flowchart of a fourth embodiment.

FIG. 20 is a flowchart of a fifth embodiment.

FIG. 21 is a graph of a Disk Drop Distance (span) as a function of test time for one example.

FIG. 22 is a graph of Disk Drop Velocity as a function of test time for the example of FIG. 21.

FIG. 23 is a graph of Disk Minimal Position as a function of test time for the example of FIGS. 21-22.

FIG. 24 is a graph of a Distance Minimum Sum as a function of test time for the example of FIGS. 21-23.

DETAILED DESCRIPTION

In the following detailed description, references are made to illustrative embodiments of methods and apparatus for carrying out the claims. It is understood that other embodiments can be utilized without departing from the scope of the claims. Illustrative methods and apparatus are described for performing blood coagulation tests of the type described above. In the context of the present application, the term “blood” means whole blood, citrated blood, platelet concentrate, plasma, or control mixtures of plasma and blood cells, unless otherwise specifically called out otherwise; the term particularly includes heparinized blood.

FIG. 1 illustrates some basic features of a possible apparatus or system, components of which are further described in U.S. Pat. No. 5,629,209, the entirety of which is incorporated by reference. A cartridge 100, having been inserted into a side 16 of a machine 10, is secured within a cartridge holder 302. An aperture 28 enables a fluid sample to be introduced into the cartridge 100 after the cartridge 100 is inserted into the machine 10. An air vent/fluid plug device 120 is aligned over a hole 304 in the base of the cartridge holder 302 to permit escape of air that is vented from the cartridge 100 during the movement of the fluid sample into its respective fluid-receiving chamber. Each fluid-receiving chamber is typically associated with an apparatus for moving a ferromagnetic material (hereinafter “disk”, e.g., a washer or the like made of a ferromagnetic material) provided by the machine 10, such as an electromagnet 122, and a position detector for detecting the position of the disk 116 within a test chamber 114, e.g., a detector 124. The term “disk” as used herein is intended to include any object of a multitude of configurations at least partially comprised of ferromagnetic material such that the disk can move within the test chamber and be lifted with the electromagnet 122. A radio frequency detector, for example, may be conveniently employed for the detector 124. It should be noted that the detector 124 is not limited to the detection of ferromagnetic material but is capable of detecting any metallic substance placed within the test chamber 114. The electromagnet 122 and the position detector 124 are connected to a circuit board 300 and thereby operatively connected to an associated computer processor (not shown) which receives information, provides directions, and calculates intermediate or final values relevant to the tests. The processor is under control of programming executed by the processor as required. For simplicity of illustration, only one fluid-receiving test chamber 114, electromagnet 122, and position detector 124 are shown. The cartridge 100 may have a plurality of such arrangements for alternative and/or comparative tests.

FIG. 2 illustrates that fluid sample 200 fills the fluid-receiving chamber and reaches the air vent/fluid plug device 120 to establish a fluid lock. The ferromagnetic disk 116 is moved between a resting position on the bottom of the fluid-receiving chamber 114 and the top of the chamber 114 as the electromagnet 122 is energized; if the electromagnet 122 is turned off, the disk 116, under the force of gravity, falls at least partially through the fluid sample 200 toward the bottom of the chamber 114. The position detector 124 measures one or more parameters (e.g., the time required for the disk 116 to fall from the top to the bottom of the chamber 114) and sends this information to the associated computer. As the viscosity of the fluid sample 200 increases, the measured time increases. Indeed, in the case of blood coagulation, eventually, the disk 116 is unable to move through a blood sample to the bottom of the test chamber 114.

When the fluid sample 200 whose viscosity is being measured is blood, the motion of the disk 116 through the blood also has the effect of activating the clotting process of the blood. The activation effect can be enhanced when the surface of the disk 116 is optionally roughened in known ways, as such techniques increase the surface area of the disk. If even faster clotting times are desired, a viscosity-altering substance may be used. For example, a clotting activator such as tissue factor thromboplastin can be added to the cartridge, or a particulate activator such as diatomaceous earth or kaolin may be used either alone or in combination with other activators such as phospholipids or tissue factors.

The position detector 124 in one embodiment is a radio frequency detector. Radio frequency detectors sense the position of the disk 116 by sensing the changes in the magnetic field surrounding the detection coil of the radio frequency detector that are caused by the presence of the disk 116. Radio frequency detectors have sensitivity to ferromagnetic and other metallic materials and resistance to effects caused by other elements of the device, such as the fluid. It should be understood, however, that other types of position detectors 124 are contemplated. For example, in another embodiment, the position detector 124 is a Hall effect sensor and its associated circuitry, as generally described in U.S. Pat. No. 7,775,976 (the entirety of which is incorporated by reference) at column 16, line 15 to column 17, line 5.

In a typical sequence, the test cartridge 100 is inserted into the side 16 of the machine 10 through the slot 26, and the disk 116 is lifted and dropped a number (e.g., three) times by electromagnet 122. This provides the average values for the minimum and maximum positions and distances that disk 116 travels without fluid sample 200. This process also serves as a system self-test to verify the functions of cartridge 100 and machine 10.

After the initial testing, a sample mix cycle begins the test protocol. The test cartridge 100 is filled with the fluid sample 200 and then the electromagnet 122 initially raises and lowers the disk 116 rapidly several times to further mix the fluid sample 200 with any viscosity-altering substance present and, if the fluid sample 200 is blood, promote activation of clotting, as discussed above. The fluid sample 200 is then allowed to rest for a short time, the duration of which depends on test type. For example, in a heparin protamine titration test, the test cycle may be initiated immediately after the sample mix cycles.

During the subsequent coagulation test phase itself, the electromagnet 122 raises the disk 116 repeatedly at a slower rate and/or reduced lifting power. After each elevation of the disk, the position detector 124 is used to determine the “fall time” (or “drop time”), i.e., the time taken for the disk 116 to fall to the bottom of the chamber 114. Absence of an increase in fall time suggests a lack of coagulation and the test continues. But an increase in fall time suggests a change in viscosity, measured in terms of the amount of fall time as compared to a baseline value. All data, including individual test results, may be displayed, stored in memory, printed, or sent to another computer, or any combination of the same. It is envisioned that the fluid viscosity testing device used with the embodiments disclosed herein can be that described above or can be a different fluid viscosity testing device that operates in a similar manner.

The geometry which underlies one possible initial clot detection algorithm is schematically illustrated in FIG. 3. The electromagnet 122, position detector 124, and fluid 200 have been omitted for clarity only. Similarly, the height of the chamber 114 is exaggerated relative to the thickness of the disk 116 only for purposes of illustration. The first embodiment of a clot detection algorithm which relies on this geometry is illustrated in the flowchart of FIGS. 4A-4B.

The clot detection algorithm 400 of FIG. 4A considers the total disk drop distance to be represented by a plurality of zones, such as four zones. The zones are not necessarily equally sized. In the embodiment illustrated, the four zones are (from top to bottom) labeled Zone 0, 1, 2 and 3. Because the total disk drop distance is determined by the geometry of the apparatus, it is determined at 410 in the following way: (1) the minimal and maximum positions of the disk are measured by the three initial lift and drop cycles before introduction of fluid 200; (2) the average values of the minimum (min) and maximum (max) are computed, and the initial disk travel distance is then calculated by the product of a factor and the difference between the maximum and minimum. The factor may be a hard-coded value slightly less than 1.0 (such as 0.91), so that the slight amount of time required for the disk to be released from the magnet is not included in the drop time; (3) the time of the disk dropping through the initial range [(0.91)×(max−min)] is measured and divided by 4 to yield a drop time for each of the four zones; (4) the end of zone positions are found by capturing the position values for each zone. The sample mix cycle is not required by the clot detection algorithm and therefore is not shown in FIG. 4A.

This embodiment thus relies on a calculation of disk velocity as the dependent variable, a value of distance as a constant, and time as the independent variable. As will be seen below, in an alternative embodiment, the roles of distance and time will be reversed.

The algorithm continues at 420 by determining the disk drop times (or, “zone counts”) of an initial number of disk drops after the sample mix cycle described above. These values are summed together for each zone in the plurality of zones. A possible value for the initial number of disk drops is four.

Next, a sensitivity scale factor (1-100%) is invoked; this value is determined separately from the disk drop times and thus it may be hard-coded into the algorithm or preset in a parameter data file. The value of the sensitivity scale factor may vary over the course of the actual test cycles (discussed further below), but in this first embodiment the sensitivity scale factor is a constant.

Once the sensitivity scale factor is invoked, the clot detection threshold for each zone is calculated at 430 as the sum of the washer drop times of the initial number of drops, multiplied by the sensitivity scale factor.

The actual clot detection process then begins at 440. During the coagulation test phase, the disk is repeatedly lifted and dropped as in the conventional process described earlier. The disk drop times are counted on a per-zone basis for each of the plurality of zones that make up the total disk drop distance, as opposed to a single measurement based on the entire distance.

The clot detection algorithm may use the outcome of any one of a plurality of criteria applied at 450 to detect a clot. A possible number of criteria is five. Any criterion may or may not depend upon the sensitivity scale factor described above. Examples of criteria which do not depend upon the sensitivity scale include three criteria which identify non-movement of the disk: (a) at 451, the disk does not drop from the top, i.e., it remains in zone 0; (b) at 455, the disk does not rise from the bottom, i.e., it remains in zone 3; and (c) at 453, the disk moves too slowly through any zone, i.e., it is moving but does not leave any of zones 0-3 in less time than a threshold value. For example, in a system such that the disk in the absence of clots would have a drop time over the entire distance on the order of 200 msec or less, that value is a suitable threshold for any one zone; if the disk spends as much time in a single zone as it would be expected to spend over the distance represented by all zones in the absence of clotting, it can be assumed that the disk is not moving due to the increased viscosity of the clotted sample.

Other criteria rely on the clot detection threshold that is derived from the sensitivity scale factor. Specifically, one criterion is that the zone counts of each of a pair of zones are greater than their respective clot detection thresholds. In another embodiment, more than one such pair of zones is established, i.e., two separate criteria of this type are considered. Such criteria may be: (d) at 453, the zone counts of zone 1 and zone 3 are each greater than their respective thresholds; and (e) at 454, the zone counts of zone 2 and zone 3 are each greater than their respective thresholds. Other combinations of zones may be selected in other embodiments. While either such criterion could be used as the (only) fourth criteria in addition to the three criteria above, they both may be used as the fourth and fifth independent criteria for detecting clot formation.

As noted before, taking all of the five criteria (a)-(e) together, any one such criterion may be used to consider a clot detected, but all five may be considered at once and any one of the five alone may be used to determine clot detection.

A second embodiment 500 is generally illustrated in the flowchart of FIG. 5. The second embodiment addresses a possible problem presented by using a constant sensitivity scale factor. If the constant value of the sensitivity scale factor is too low, false detection is possible, particularly during the initial test cycles when disk movements are not yet stabilized. This is because dry kaolin that is not fully mixed and dispersed during the initial mix cycle interferes with accurate assessment of the disk drop rates early in the test phase. However, if the value is too large, weak clots (i.e., clots which do not produce significant change in viscosity) may not be detected at all, particularly later in the test phase when the amount of unmixed dry kaolin is reduced by subsequent agitation during prior portions of the test phase.

To address this, the sensitivity scale factor (1-100%) may take on different values during different portions of the coagulation test phase in this second embodiment, as opposed to the first embodiment above, in which the sensitivity scale is a constant throughout the test phase.

In an approach to this second embodiment, as illustrated schematically in FIG. 6, the coagulation test phase is divided into smaller periods; as illustrated, the entire coagulation test phase is divided into three test periods which are labeled 1, 2 and 3. The duration of each coagulation test period is either hard-coded into the algorithm or is a value obtained from a parameter file at 510.

At 530, the clot detection threshold or end point is determined for each of the three periods. During the initial period, Test Period 1, which may be on the order of 0 seconds to a value in the range of 30 to 100 seconds, the clot detection sensitivity scale factor, F₀, may be obtained from a parameter file. A transition period, Test Period 2, begins at the end of Test Period 1 and may extend to a value on the order of 400 to 500 seconds in total elapsed time. During Test Period 2, the sensitivity scale is reduced from the initial value of F₀. The rate of reduction may be obtained from a parameter file. In general, the rate of reduction could be a constant value or a function of time or other parameters, such as an exponential decay. An exponential decay provides for a smoother transition. The final period, Test Period 3, begins at the end of Test Period 2 (if present, as illustrated) and extends to the conclusion of the test, typically 999 or 1,000 seconds. During Test Period 3, the sensitivity scale is constant at the reduced value F₁ which results from the steady reduction of the threshold value from F₀.

Thus, over the course of the three test periods, the sensitivity scale factor is relatively high during the first test period, which is typically when compounds (e.g., kaolin) are mixing with the blood and the washer location has not yet stabilized. The relatively high value avoids false detection of clots during such mixing. The lowered sensitivity in the third test period allows detection of weak clots. In the broadest implementation, only the initial and final (first and third) test periods are required; all that is required are relatively high and low values of the sensitivity scale factor. However, the second transition test period after the initial and before the subsequent final period will ensure a smooth transition between the two values. Although not illustrated here, additional periods (fourth, fifth, etc.) and scale factors values are possible but not required by this embodiment of the clot detection algorithm.

After the threshold value is determined for the current test period, the clot detection algorithm 450 is employed as described above.

Example 1

FIG. 6 shows an example of disk drop time monitored during a NG-HMS HR-ACT test as generally described above. This example shows how a clot is detected via the modified clot detection algorithm. In this example, a clot is detected by comparing disk drop times measured in Zones 1, 2 and 3 against the clot detection thresholds of their respective zones.

The pertinent data and parameters are summarized below in Table 1. Initial threshold values were established at 30 seconds after the beginning of the test phase and final threshold values were established at 400 seconds (i.e., the transition period was 370 seconds in duration). The reduction in the threshold values was exponential at the rate indicated.

TABLE 1 Sum of Percentage Final Zone Four Initial Initial Final Final Reduction Count at Time Initial Four Values Zones Scale Threshold Scale Threshold in Threshold of Clot Zone (msec) (msec) Factor (msec) Factor (msec) from Initial Detection 0 24 24 24 24 96 75% 72 0.4884 46 45% 65 1 40 40 40 40 160 75% 120 0.4884 78 43% 82 2 45 45 45 45 180 75% 135 0.4884 87 44% 68 3 35 35 35 35 140 75% 105 0.4884 68 43% 83

The data in the above table shows the drop times for the initial four drops in the each of the four zones. The drop times are scaled to the initial sensitivity scale factor to produce the initial threshold. As the scale factor is attenuated down, the threshold decreases for each zone (by 27% in this example). At the time of clot detection, the zone counts for Zone 1 and Zone 3 exceed their respective thresholds, and thus the criterion 453 (see FIG. 4B) has been met. Therefore, clot detection (end point) is triggered.

The data in this example shows that the disk drop times in each of the four zones generally decreased over the initial 400 seconds, then increased afterward. This is consistent with the dispersion of dry kaolin during the early portion of the test period. Kaolin reagent is not fully dispersed during the mixing period and therefore initially produces a longer drop time. When the kaolin is fully dispersed, the drop time decreases. After clot formation, the drop time increases (this is also illustrated in the data of FIG. 8). This illustrates why the individual zone threshold value needs to set high in the early portion of the test period, so that the change in washer drop time caused by dry kaolin dispersion will not generate false clot detection. After the 400 second mark, as the threshold values are held constant at their respective reduced values, the increased washer drop times exceed the zone threshold values in Zones 0, 1, and 3 after a cumulative time of approximately 750 seconds. The criteria for clot formation are met because the threshold values in both Zones 1 and 3 are exceeded. In fact, for this specific data, in every case, the zone counts 700 exceeded the clot detection thresholds 710 during Test Period 3. This provides further support that alternative clot detection criteria could be formed from combinations of conditions other than those listed above.

A third embodiment is best explained with the following comprehensive description which repeats some of the description of the first two embodiments. However, this is solely for convenience and should not be understood to limit the scope of any embodiments of the invention in any manner. Thus, as before, the instrument or machine 10 is designed to measure the clotting capability of a patient's blood. The measurement is expressed as the amount of time it takes for a freshly drawn sample of blood to clot. The instrument operates using a disposable cartridge 100 that can hold a small amount of blood. The instrument keeps the cartridge 100 and blood sample 200 at a temperature equivalent to normal human body temperature. The cartridge 100 contains chemicals that accelerate the clotting of blood 200 in a known manner, so a clotting test can be completed quickly. The blood is injected at a syringe fitting on the cartridge, and fills a number of separate channels in the cartridge. In each channel, there is a well containing a metal disk or washer 116. The disk 116 is free to move up and down within the well 114. For each channel, the instrument has an electromagnet 122 positioned above the well that can be activated to lift the disk, or deactivated to drop the disk 116. There is also an inductive sensor 124 positioned below the well that can measure the vertical position of the disk in the well, and a capacitive sensor that detects when the well is full of blood.

To run a test of a blood sample's clotting capability, an operator will insert a fresh, unused cartridge 100 in the instrument and inject the blood 200. The instrument 10 then repeatedly accesses the electromagnets 122 to lift and drop each disk 116, while monitoring the disk position sensors 124 to evaluate the resulting movement of the disk. When the blood is first injected, each disk should be seen to freely move up and down in the well. As a test progresses and clots start to form in the blood, the movement of each disk should be seen to slow or stop due to interference from the clots. When the blood clots, the instrument outputs the elapsed test time that was required to achieve the clot. This is the desired measure of the blood sample's clotting capability.

There may be a number of different cartridge types used with the instrument. If so, typically each type has a specific mixture of chemicals designed for a specific type of clotting test. Some cartridge types use all channels, while others use only some of the channels. To support different cartridge types (if present), the instrument may be multi-functional, i.e., the operational methods (or “algorithm”) performed by the computer processor connected to circuit board 300 may be parameterized. For example, numerous aspects of disk control and measurement are driven by configurable parameters. For each cartridge type, there is a unique set of predefined constants used to initialize the parameters when that cartridge is used. Key parameters that drive a test may present tradeoffs in setting the parameters for a specific type of cartridge. The system may have a separate copy of the cartridge configuration parameter settings for each defined cartridge type. The cartridge type may be indicated by a cartridge code number. The instrument may read or otherwise detect the number (e.g., by reading a bar code or similar indicia, or by other techniques) from the cartridge after it is inserted into the system.

As noted above, operation of the instrument involves both control of a disk (lift and drop), and measurement of the resulting disk behavior (e.g., span of distance traveled and velocity of drop). As before, fundamental terms for disk control and measurement may be defined.

Referring in addition to FIG. 9, a disk or test cycle is a time period over which a disk is lifted by the electromagnet, held at a disk maximum position for a while, and then dropped and allowed to settle at the Disk Minimum Position. In many instances, the Disk Maximum Position may be proximate the top of the well. The lift portion of the cycle is the period of time from the beginning of the cycle until the disk is dropped. At the beginning of the lift, the electromagnet is activated with enough power to pull the disk up from within the well. Then the power is reduced to a minimal level to hold the disk at the disk maximum position. The power is reduced to zero to drop the disk.

Referring also to FIG. 10, during a disk cycle, the position sensor is accessed to determine values relating to the span of travel of the disk, such as Disk Maximum Position/Distance Maximum (the vertical distance of the disk just before it is dropped), Disk Minimum Position/Distance Minimum (the vertical distance of the disk after it is dropped and settles), and Disk Drop Distance or disk Distance Span (the difference between Distance Maximum and Distance Minimum). Over the course of a test, a decrease in the disk Distance Span is an indication that clots are forming and interfering with the span of travel of the disk through the fluid sample.

Turning to FIG. 11, also during a disk cycle, the position sensor is accessed to determine values relating to the velocity of the disk during the drop, including Disk Drop Velocity (vertical distance dropped over a fixed Drop Measurement Time elapsed after the disk drops below a Top Separation Threshold). Since this value is computed as a distance traveled per unit of time, it can be called a velocity measure. The Top Separation Threshold and Fixed Drop Measurement Time are set to appropriate values during a Clot Test Calibrate operation as described further below.

As defined here, the Disk Drop Velocity is only a rough measure of the speed at which the disk dropped, but can be a reliable indicator of when the drop is being slowed by increasing viscosity of the blood sample due to clotting. An instantaneous measure of the disk speed is considered to be a less valuable indicator of clots, because it can vary widely among drops (even in the same sample at the same relative point in the disk cycle), due to variation in the way the disk drops (e.g., variation in the amount of time it takes to separate from the electromagnet, and/or variation in the angular orientation of the disk during the drop). These variations have a large effect on instantaneous speed measurements, but only minimal effect on the rough measure of speed. The velocity of the disk is of interest only during the drop portion of the cycle. During a drop, the force on the disk is its weight due to gravity, which is consistent from drop to drop. Thus, changes in the Disk Drop Velocity (disk velocity) from drop to drop are directly due to changes in viscosity of the blood. During a lift, the force on the disk varies widely due to variations in its distance from the electromagnet, electromagnet power, angular orientation of the disk, etc. Thus, changes in disk velocity from lift to lift are not always due to viscosity changes alone. For this reason, it is possible to forego measurements of the disk velocity during the lift. Use of the Disk Drop Velocity measure also provides more information about the state of the blood sample than the disk Distance Span measure alone. The disk may continue to have the full span of travel from the top of the well to the bottom, but may slow significantly on the drops to the bottom. For some clot test types, the use of Disk Drop Velocity is critical to declaring the sample clotted at the correct elapsed test time.

Turning to FIG. 12, the Disk Scale is a set of scaling values relating to control of the disk during the lift. They determine how hard the electromagnet pulls on a disk during the lift portion of a cycle. The Disk Scale consists of the following values: Estimated Distance Span (the estimated distance span of the well), Distance At Lift Start (the distance value at the well bottom), Hold Power (the setpoint of the electromagnet power level after the high power lift is complete), and Lift Power Ticks Max (the maximum number of milliseconds in which electromagnet power can be set higher than the Hold Power at the beginning of the lift portion of a cycle). Several other remaining values allow for setting the electromagnet power higher than the Hold Power when the vertical distance of the disk is at a value lower than the top of the well. They include Lift Zone 0 Distance Span Max (span of distance from the well bottom comprising lift zone 0), Lift Zone 0 Power (setpoint of electromagnet power level when the disk is in lift zone 0), Lift Zone 1 Distance Span Max (span of distance from the well bottom comprising lift zone 1), Lift Zone 1 Power (setpoint of electromagnet power level when the disk is in lift zone 1, and not in zone 0), Lift Zone 2 Distance Span Max (span of distance from the well bottom comprising lift zone 2), and Lift Zone 2 Power (electromagnet power level to set when the disk is in lift zone 2, and not in zones 0 or 1). Other similar values can be established when there is a different number of zones.

The lift zone power levels are meant to be applied for only a brief period of time (for example, approximately 10 msec) to pull the disk to the top of the well. Once the disk is higher than the Lift Zone 2 Distance Span Max, the electromagnet power level is set to a Hold Power value. If the disk never gets higher than Lift Zone 2 Distance Span Max, the power is switched to Hold Power after the time period defined by Lift Power Ticks Max. Power levels higher than Hold Power are only allowed to be set for one cartridge channel at a time. The instrument sequences the channels one at a time to perform the disk lifts. The restrictions on electromagnet power ensure that the magnets do not generate heat in an amount sufficient to interfere with control of the blood sample temperature. The instrument may use a heater control loop to keep the blood sample at normal human body temperature.

Different settings of Disk Scale are used during the different phases of operation of a test (Cartridge Test, Mix, and Clot Test). The settings are changed to suit the purposes of the test phase. For example, during the mix phase, high power levels are used during the lift to agitate the blood for mixing with the dry chemicals in the cartridge. During the clot test phase, lower power levels are used so that lifting of the disks will not interfere with clot formation.

The instrument goes through three phases of operation to perform a test of a blood sample's clotting ability: Cartridge Test, Mix, and Clot Test.

When a cartridge is inserted into the instrument, the instrument performs a Cartridge Test to verify the disks all have a sufficient span of travel. The Cartridge Test consists of a series of steps. First, the Disk Scale is set to values appropriate for lifting the disks inside an empty cartridge (fluid sample not yet added). The Estimated Distance Span value for each disk is set to a defined constant value, because there is no previous cycle data for this cartridge to give a better estimate. Next, a series (e.g., three) of Disk Cycles is performed. For each Disk Cycle, the following data are gathered and saved for each disk drop: Distance Minimum Position, Distance Maximum Position, and Distance Span. To pass the Cartridge Test, the data for each disk drop must conform to the following criteria: (1) each Distance Span must be greater than a defined minimum value; and (2) the maximum variation between any Distance Span and the largest Distance Span must be less than a defined maximum value. If the Cartridge Test passes, the average of the Distance Span values for each disk is saved, to be used as the Estimated Distance Span for the later test phases.

After the Cartridge Test, the instrument waits for the cartridge to be filled with blood by the operator. The fill sensors are polled until they indicate all channels are filled. When all channels are filled, the instrument begins the Mix phase of the test.

The purpose of the Mix phase is to agitate the blood in order to mix it with the dry chemicals contained in the cartridge wells. The Mix phase consists of the following steps. First, the Disk Scale is set to values appropriate for aggressively lifting the disks inside a blood-filled cartridge, and the Estimated Distance Span value for each disk is set to the average of the Distance Span values measured during the Cartridge Test. Next, Disk Cycles are performed for the time duration allocated for the Mix phase. The Elapsed Test Time begins counting at the beginning of the Mix phase. Later, when clotting is detected, the clotting time will be reported as the time since the beginning of the Mix phase.

In the Clot Test phase, the disks are lifted and dropped for the sole purpose of detecting when clots have formed in the blood. The Clot Test consists of the following steps. First, the Disk Scale is set to values appropriate for gently lifting the disks inside a blood-filled cartridge, and the Estimated Distance Span value for each disk is set to the average of the Distance Span values measured during the Cartridge Test. Next, Disk Cycles are performed for the time duration allocated to the Clot Test phase. For each cycle, various disk measurement data for each disk are temporarily saved. These include distance data for each 1 msec time increment of the first 500 msec of the drop portion of the cycle, if applicable. At the end of each cycle, the disk measurement data can be used for a variety of purposes including a Clot Test Calibrate (in which the data is used for computing calibration values representing Distance Span and Drop Velocity of the blood sample in a normal unclotted state) and Clot Test Evaluate (in which the data is used for computing Distance Span and Drop Velocity for comparison against the calibration values, to determine if the blood sample has reached a clotted state). (Further details of Clot Test Calibrate and Clot Test Evaluate are discussed below.) The calibration data consists of three cycles worth of disk measurement values.

The decision about whether to use the disk measurement data for Clot Test Calibrate or Clot Test Evaluate is made as follows. If this is one of the first three cycles, then use the data for Clot Test Calibrate; but if this is not one of the first three cycles, but the current Distance Span is greater than the smallest Distance Span in the saved cycles of calibration data, then replace that cycle of Distance Span data with the current Distance Span for Clot Test Calibrate. This is necessary because the Distance Span can increase over the initial cycles of the Clot Test phase, as the dry chemicals continue to dissolve and allow for a greater span of travel of the disk. The calibration Distance Span must be recomputed to prepare for any clotting that occurs after this point. The calibration Drop Velocity is not changed from the value computed over the first three cycles. When replacing a Distance Span and redoing Clot Test Calibrate for the span, it is possible to follow that replacement with a Clot Test Evaluate. Since the new Distance Span is larger than the calibration value it replaced, it is unlikely that a clot will be detected due to a change in Distance Span, but a clot could be detected due to a change in Drop Velocity. If neither of the above two criteria are met, then the data is used for Clot Test Evaluate.

The purpose of the Clot Test Calibrate operation is to compute calibration values of Distance Span and Drop Velocity that represent normal values for the blood sample in an unclotted state. These values are best not computed until there are at least several (e.g., three) cycles of Clot Test drop data to analyze. In the case of three cycles, the calibration value for Distance Span is computed from the three available cycles of distance span data by taking the Distance Span calibration value as equal to the Largest Distance Maximum over the three cycles less the Smallest Distance Minimum over the three cycles. When a different number of cycles is used, an analogous calculation may be made. The calibration value for Distance Span is recomputed at every cycle where the new value of Distance Span is larger than one of the three values used for the previous computation of the calibration Distance Span. This is necessary because the Distance Span tends to increase during the early part of the Clot Test phase, as the chemicals in the cartridge well become fully dissolved. The calibration value for Drop Velocity is computed by analyzing the first three cycles of Clot Test drop data. The calibration value for Drop Velocity is computed only once for each disk. It is not changed when the calibration value for Distance Span is recalculated on a later cycle due to an increase in span.

Referring now to FIGS. 13 and 14, the Drop Velocity is a rough measure of the speed at which the disk drops from top to bottom of the well. To compute the calibration value, the drop data is analyzed in multiple (e.g., two) passes. This allows the Drop Velocity measurement to be scaled to the characteristics of the specific cartridge well and fluid sample being used; the way that a disk drops can be quite different in one sample containing a whole blood fluid versus another containing only blood plasma. In the first pass, the (three) cycles of disk drop measurement data are examined to determine the Measured Drop Time for the disk to fall from top to bottom. To isolate this measurement from the normal signal noise of the position data, only a portion of the drop is considered. The Measured Drop Time is computed as a time that elapses after the disk falls below a Top Separation Threshold and before it enters a Bottom Separation Threshold. The Top Separation Threshold and Bottom Separation Threshold are computed from cartridge configuration parameters that define them as a percentage of the Distance Span. (Note that, while this implicitly creates three regions in the well, these should not be confused with the Zones established in the alternative embodiment discussed above.) The average of the Measured Drop Time values over the (three) cycles is used as the Fixed Drop Measurement Time for the second pass.

In the second pass, a Drop Velocity value is computed for each of the (three) cycles of drop data. Each Drop Velocity is computed as the vertical distance dropped over a Fixed Drop Measurement Time elapsed after the disk drops below a Top Separation Threshold. The calibration value of Drop Velocity is then set to a representative value, such as the largest of the Drop Velocity values computed over the (three) cycles of drop data. (In other variations, the representative value could be the average or mean of the values.) The Fixed Drop Measurement Time and Top Separation Threshold are saved for computing Drop Velocity values in Clot Test Evaluate operations throughout the remainder of the Clot Test.

It bears repeating that this embodiment, in contrast to the “Zoned” embodiment discussed above, relies on a calculation of disk velocity as the dependent variable, taking distance as the independent variable and time (specifically the Fixed Drop Measurement Time value) as a constant.

In order to pass the Clot Test Calibrate, the data for each disk must conform to the following: each Distance Span must be greater than a defined minimum value, the maximum variation between any Distance Span and the largest Distance Span must be less than a defined maximum value, each Drop Velocity must be greater than a defined minimum value, and the maximum variation between any Drop Velocity and the largest Drop Velocity must be less than a defined maximum value. If the Clot Test Calibrate fails, then the channel will be indicated as already being clotted. Otherwise the channel will continue to be processed in the Clot Test phase.

The purpose of the Clot Test Evaluate operation is to compare the current values of one or both of Distance Span and Drop Velocity to their respective calibration values, to determine if the channel is clotted. The exact criteria used when comparing the current values to the calibration values are specific to each cartridge type, and are therefore defined in the Cartridge Configuration Parameters when that approach is employed. Specifically, the Cartridge Configuration Parameters define which one of the following sets of changes must occur in order for a channel to be declared clotted: (1) if Distance Span drops below a threshold value, defined as a percentage of the calibration Distance Span; (2) if Drop Velocity drops below a threshold value, defined as a percentage of the calibration Drop Velocity; (3) if either Distance Span or Drop Velocity drops below its respective threshold value, i.e., either (1) or (2); and (4) if both Distance Span and Drop Velocity drop below their threshold values, i.e., both (1) and (2). Once a channel is declared clotted, its elapsed clotting time is captured and the channel no longer undergoes Disk Cycles in the Clot Test phase.

For either Distance Span or Drop Velocity, one variation is to require that the clot detection threshold be reached for a number of consecutive cycles before a clot is declared. In that case, a further option is to use a specific one of those cycles as the cycle representing the elapsed clotting time. With this feature, a single low measurement of Distance Span or Drop Velocity might not result in a reported clot, but if that measurement persists for a number of consecutive iterations, then the first occurrence of the measurement could be indicated as the clotting time or end point. This is a way to guard against an anomalous event that might affect the measurement of a single cycle.

Other aspects of the first and second embodiments discussed above are also applicable to this third embodiment. For example, over the course of the test it is possible to do any or all of: change (especially, to increase) the cycle times, change lift power levels, and change clot detection thresholds, for the same reasons as noted above and using the same or equivalent techniques. For example, the clot detection sensitivity scale factor, or any other parameter relevant to at least one of the plurality of criteria used to determine clot formation, may be changed in a manner analogous to that illustrated in FIG. 6. This includes optional variations such as holding the parameter equal to a first constant value during an initial period of the plurality of periods, and at a second constant value (lower than the first constant value), during a subsequent third period of the plurality of periods; the initial period and the subsequent period may be separated by a transition period during which the parameter is reduced from the first constant value to the second constant value. The parameter may be reduced during the transition period at a constant rate, or exponentially, during the transition period.

FIG. 15 is a summary 600 of this third embodiment as described in detail above, in a flowchart form analogous to that of FIG. 5 for the second embodiment. At 610, the disk drop distance is found and divided into lift zones. At 620, the disk drop time is found and thus the disk drop velocity is computed. Separately, at 625, the test cycles are divided into test periods. These two inputs enter step 630, in which the disk drop distance and velocity values are updated if appropriate, and then into 640 in which the disk drop distance and/or velocity are compared to their respective threshold values. Based on such comparison(s), the decision 650 is made whether to consider the clot detected or to continue the testing (updating values as noted before).

FIGS. 16-17 illustrate the importance of considering either or both of disk travel distance (span) and velocity, depending on the assay and identity of sample fluid being tested. Each figure is a pair of graphs comparing results of test measurements related to the third embodiment. FIG. 16 illustrates measurements of disk travel distance (span) on the left and disk velocity on the right, both measured in plasma from a common sample and in the same channel of a test apparatus. As can be seen, the steep and sudden decrease span and velocity after approximately forty-five seconds demonstrates that either parameter could be used to detect a clot, and further that the combination of the two parameters could be also be used. By contrast, FIG. 17 is a similar illustration of those two parameters in samples of fresh whole blood (“FWB”), again in a common channel. A comparison of the two graphs shows that even if span length remains essentially unchanged (left graph), a sudden decrease in disk velocity (right graph) may be used alone to signal clot formation.

FIG. 18 compares the drop delay time (i.e., the time in the top separation zone) between samples of FWB (on the left) and plasma (on the right) in different channels. It illustrates that the former is relatively insensitive to change with time, even times as long as nearly 150 seconds; whereas the latter exhibits a sudden and dramatic increase from a very stable value (approximately 30 msec on average) after approximately 50 seconds of test duration. The results show that the disk drop delay time is dependent on viscosity because the values are significantly greater for FWB than for plasma. The average fixed drop measurement time in the unclotted plasma in this example was 40 msec and for the unclotted FWB it was 107 msec.

Referring now also to a fourth embodiment 701, which is summarized in FIG. 19 and utilizes many processes, principles and equipment discussed above. At step 709, the test cycles are optionally divided into a plurality of test periods (e.g., two, three or more). At step 712, a Disk Drop Distance (disk Distance Span) is determined and the disk Distance Span is optionally divided in a plurality of zones (e.g., three) as described above with respect to prior embodiments. To conduct a coagulation test cycle, the disk is dropped from an initial or first Disk Maximum Position, which may or may not be proximate the top of the test chamber. As with prior embodiments, the first Disk Maximum position is the highest point at which the disk is positioned during the respective test cycle. After releasing the force maintaining the disk at the first Disk Maximum Position, the disk falls through the test fluid via the force of gravity to a first Disk Minimum Position, which is measured (e.g., with a position detector) at the lowest point in which the disk settles. The disk is then dropped again from a second Disk Maximum Position after a specified period of time (either after lifting the disk or from its current position as discussed in further detail below). After the disk settles, a second Disk Minimum Position is measured.

Lifting of the disk at the end of each test cycle can be specified by test cycle duration time. The test cycle duration can be from about 0.5 seconds to about 10 seconds, depending on the test needs. For example, if test cycle duration is 1 seconds, then a 999 second test is divided up 999 test cycles. For each test cycle, a portion of time is used for disk lift, and the remaining portion is for disk drop. For example, for 1 second test cycle duration, 0.5 seconds can be used for disk lift and the remaining 0.5 seconds can be used for disk drop. If the disk did not drop to the bottom of the well from the previous test cycle, in the next test cycle, the disk can optionally start at the position from the last test cycle. Therefore, the starting position can depend on test cycle duration and fluid sample viscosity. The starting position can potentially be at the bottom, or somewhere in the middle of the well or even at the top of the test chamber well. It can depend on how the assay is programmed. In some assay, the test duration and time distribution for lift and drop are programmed so that the disk would start at the previous Disk Minimum Position or bottom of the well at each test cycle (unless clot formed and disk is immobilized by the clot); in other assay, the test duration and time distribution for lift and drop are programmed so that the disk would start from the top of the well or Disk Maximum Position at each test cycle.

A plurality of (e.g., three) preliminary test cycles are conducted to obtain a lowest Disk Minimum Position and a highest Disk Maximum Position among the preliminary (e.g., first three) test cycles. From this information, a Reference Disk-Span (i.e. the highest Disk Maximum Position minus the lowest Disk Minimum Position) and a Reference Disk Minimum Position (i.e. the lowest measured Disk Minimum Position) are obtained. A Clot Detection Reference for the Disk Minimum Position is computed at step 714 by the following formula: the Clot Detection Reference (for Disk Minimum Position)=Reference Disk Minimum Position+(X %×Reference Disk-Span). X % is a pre-selected threshold coded between 0 and 100% in assay protocol to adjust the Clot Detection Reference based on Disk Minimum Position. The Reference Disk Minimum Position and the Reference Disk-Span are updated in step 716 for the next test cycle if a new lowest in Disk Minimum Position or a new highest in Disk Maximum Position are measured, and a new Clot Detection Reference is computed and updated. If no new lowest Disk Minimum Position or no new highest Disk Maximum Position is measured, the Reference Disk Minimum and the Reference Disk-Span remain the same as at step 714, and the Clot Detection Reference is not changed from step 714. The Disk Minimum Position of is compared at step 718 to the latest (most recent) Clot Detection Reference. At decision step 720, if the value of the Disk Minimum Position is greater than (>) the present Clot Detection Reference, clot detection is declared at 722. If the value of the Disk Minimum Position is less than (<) the present Clot Detection Reference, continue to update the reference Disk Minimum Position and the Reference Disk-Span for the next test cycle at step 716, and compute the most recent Clot Detection Reference, and evaluate the measurements obtained from the new test cycle against the new or most recent Clot Detection Reference until clot detection is declared or the test otherwise concludes. To avoid false detection of a clot, the clot test continues for three or more test cycles (specified in assay protocol) when “>” condition is met at 720. If all of Disk Minimum Positions for three continuous test cycles meet the “>” Clot Detection Reference condition, clotting time is concluded from the first “>” test cycle. If the Disk Minimum Positions for three test cycles failed to meet the “>” Clot Detection Reference condition, then clot is not declared and test continues.

The pre-selected threshold X % used for calculating the Clot Detection Reference can vary, depending on the test period, as desired. In one example embodiment, the pre-selected threshold (X %) is not capable of determining a clot for the first time period for seconds 0-250 (e.g., X % can be set at 40% or more) and the pre-selected threshold (X %) for the second time period for seconds ˜250-450 is 10% and the pre-selected threshold (X %) the third time period for the remainder of the coagulation test after 450 seconds is 8%.

As stated above and as illustrated in FIG. 19, the Disk Minimum Position can be only one of many parameters repeatedly measured 724 and updated 716 for comparison to corresponding clot detection threshold pre-set by assay protocol for the respective time period 718. In this way, a clot can be detected and the test can be concluded if any one of the plurality of parameters assessed (e.g., any or all of the first-fourth embodiments) exceeds the respective clot detection threshold. Clot detection thresholds, references or the conditions at which a clot will be detected for other assessed parameters can be assigned in manners discussed above with respect to other embodiments.

Referring now also to a fifth embodiment 800, which is generally outlined in FIG. 20. In this embodiment, the measured Disk Minimum Position values are also assessed, but in a different way. In this embodiment, the initial setup and test cycles of steps 810-812 can be conducted as described with the fourth embodiment 710-712, and the lowest measured Disk Minimum Position is assigned as the Reference Disk Minimum Position 814 (as in the fourth embodiment at step 714) and the Reference Disk-Span is calculated as the lowest Disk Maximum subtracted from the highest Disk Maximum (also as in the fourth embodiment at step 714). However, to determine whether a change in Disk Minimum Position in a particular test cycle is significant enough to be considered as a potential clotting event, an Enabling Threshold (Y %) to start integrating disk minimum position change is used to compute a Reference for Enabling Integration of Disk Minimum Position Change at step 814 using the following formula: Reference for Enabling Integration of Disk Minimum Position Change=Reference Disk Minimum Position+(Y %×Reference Disk-Span). The Reference Disk Minimum Position and/or the Reference Disk-Span are updated at step 816 if a new lowest Disk Minimum position or a new highest Disk Maximum position is found or measured as additional test cycles are conducted, and a new Reference for Enabling Integration of Disk Minimum Position Change is computed. If no new lowest Disk Minimum Position or a new highest Disk Maximum Position are found, the reference Disk Minimum Position and the Reference Disk-Span remain the same as step 814, and the Reference for Enabling Integration of Disk Minimum Position Change is not changed from step 814. The Enabling Threshold (Y %) to start integrating changes in the Disk Minimum Position is used to eliminate any Change in Minimal Position (present Disk Minimum Position minus the lowest measured Disk Minimum Position) caused by changes (i.e. noise) not associated to clot formation, such as possible sensor signal drift. Y % can be anywhere between 0 to 100%. In one example, the Enabling Threshold preset by assay protocol is a 2% increase (or about 2%) in Reference Disk-Span from the lowest measured Disk Minimum Position. The Disk Minimum Position is compared to the latest Reference for Enabling Integration of Disk Minimum Position Change at step 818. At decision point 820, if the Change in Minimal Position is below the Reference for Enabling Integration of Disk Minimum Position Change calculated at step 814, a Disk Change Value is set at zero or the Change in Minimal Position is otherwise disregarded as not indicating a potential clotting event. When the Change in Minimal Position is above the Reference for Enabling Integration of Disk Minimum Position Change at step 820, then the Disk Change Value is computed at step 822 as the current Disk Minimum Position subtracted from the most recent calculated Reference Disk Minimum Position. The current Disk Change Value for each cycle is added to each of the previous Disk Change Values to calculate a Distance Minimum Sum 822-824. The Distance Minimum Sum is compared with a Clot Detection Reference computed as Z %×Reference Disk-Span at step 826 and Z % is a Clot Detection Threshold pre-set by assay protocol for the respective time period. If the Distance Minimum Sum is above the Clot Detection Reference at step 828, a clot is detected 830. If the Distance Minimum Sum is below the Clot Detection Reference at step 828, a clot is not indicated to be detected and the test continues. If enabled for the respective time period, the Disk Change Value of the most current test cycle is added to the Disk Change Values (previous Distance Minimum Sum) of the subsequent test cycles to continually update the Distance Minimum Sum until a clot is detected. In one example embodiment, the Change in Minimum Position or Distance Minimum Sum are not assessed or capable of determining a clot for the first time period for seconds 0-250 and the Clot Detection Threshold for the first time period for seconds ˜250-450 is 40% of the lowest measured Disk Minimum Position and the Clot Detection Threshold for the third time period for the remainder of the coagulation test is 25% of the lowest measured Disk Minimum Position. Therefore, the Clot Detection Threshold is variable based on both the time period and the results of the test cycles conducted.

As indicated in FIG. 20 at steps 832 and 824-826, in some embodiments, the Distance Minimum Sum is assessed concurrently or otherwise in combination with one or more of the previously disclosed embodiments/parameters of the first through fourth embodiments in the manner as disclosed above. The one or more parameters can optionally be assessed dependent of the test period of the coagulation test phase. For example, in one illustrative embodiment, the test period is divided into three test periods as in the fourth embodiment. The start time for enabling the modality of the fifth embodiment could be any time after test cycle started (after the Mix phase), but in some embodiments, the fifth embodiment is not enabled and is not assessed to evaluate clot formation until the coagulation test phase is in a test period in which at least 250 seconds has elapsed (e.g., the second test period). In test period(s) including test cycles prior to 250 seconds and also during test period(s) after 250 seconds, the modalities of the first-fourth embodiments disclosed above can be optionally assessed in any combination, as desired. A clot can be detected and the test can be concluded if any one of the plurality of parameters assessed (e.g., any or all of the first-fifth embodiments) exceeds the respective clot detection threshold.

Example 2

FIG. 21 plots the results of an example of repeatedly monitoring changes in the disk Distance Span as a function of the elapsed time during a NG-HMS HR-ACT test as generally described above. The raw data used to plot FIG. 21 is provided in Table 2 provided below. In the present example, the target Activated Clotting Time was 514 seconds. It can be seen that noise 902 (generally referenced) due to factors other than clot formation is present at the start of the test, prior to formation of an actual clot as generally referenced at 904. If the clot formation threshold is set low, this noise 902 can surpass the low threshold, triggering a clot detection prematurely (i.e. false clot detection). In the present example, the clot detection threshold was set to a 20% reduction as compared to the previous test cycle for seconds 0-450 seconds and a 10% reduction as compared to the previous test cycle for test cycles occurring after 450 seconds. In assessing this modality, a clot was detected at 534.7 seconds.

Similarly, FIG. 22 plots the results of monitoring changes in the disk Drop Velocity as a function of test time during repeated test cycles as further discussed above. Once again, if the clot detection threshold is set low, noise 1002 (generally referenced) at the beginning of the test would have triggered the clot detection premature to formation of an actual clot as generally referenced later in the test at 1004. Conversely, if the clot detection threshold is set to be higher as to exclude the noise, early detection of the forming clot would not be achieved. In the present example, the clot detection threshold was set to a 20% reduction as compared to the previous test cycle for seconds 0-450 and a 10% reduction as compared to the previous test cycle for after second 450. A clot was detected at 730.3 seconds. The raw data used to plot FIG. 22 is also provided in Table 2 below.

As illustrated above, evaluating only changes disk Distance Span and disk Drop Velocity can fail to detect the clot formation at an early stage in the clot formation process. The present inventors have found that by evaluating changes in the Disk Minimum Position either individually or in combination with one or more of the first-third embodiments, noise is smoothed out in the plotted test data so that noise does not trigger false detection of a clotting event while still providing early detection of a clot.

In support of this theory, the test results provided in Table 2 were plotted to evaluate the measured Disk Minimal Position as a function of test time in FIG. 23. In this embodiment, the coagulation test phase is broken up into three test periods. One period being seconds 0-250, the second test period being between seconds 250-450 and the third test period being after second 450. The Clot Detection Threshold was set such that if the Disk Minimum Position is at least 10% increase from the initial, first Disk Minimum Position during the second time period, clot detection is triggered and in the third time period, a Disk Minimum Position greater than 8% will trigger clot detection. Therefore, the Disk Minimum Position is not assessed or capable of triggering clot detection in the first test period. In this example, the Disk Minimal Position exceeds the 8% increase threshold for the second time period, at second 560.8, which triggers clot indication.

The graph of FIG. 24 shows how a clot is detected in the test of Table 2 by assessing the Distance Minimum Sum as a function of time, which increases the sensitivity of the test as compared to the method of FIG. 23. In this example, the Reference for Enabling Integration of Disk Minimum Position Change is set to be a 2% increase as compared the lowest measured Disk Distance Minimum. The Clot Detection Threshold is set such that if the Disk Change Value increases at least 40% as compared to the lowest measured test cycle during seconds 0-450 (first time period), clot detection is triggered and after second 450 (second time period), an increase in the Disk Change Value greater than 25% as compared to the lowest measure test cycle will trigger clot detection. In this example, Table 2 indicates that clot detection is triggered at 521.7 seconds, which is also associated with a spike (signal) as seen plotted in the graph. Therefore, the modality of FIG. 24, of the four modalities of FIGS. 21-24, provided the earliest detection of the clot and also provided clot detection closest to the target ACT of 514 seconds.

While the description above uses the procedures and values of clot detection methods to describe certain details, the broadest scope of the disclosure includes physical representations of that algorithm or methods (such as an apparatus which relies on any combination of analog or digital hardware to implement the same), as well as methods of carrying out the algorithm and methods that do not depend upon the specific physical components mentioned above but nonetheless achieve the same or equivalent results. Therefore, the full scope of the present disclosure is described by the following claims.

TABLE 2 COAGULATION TEST Fill Dist Dist Dist Dist Span Drop Vel Drop Dist Min Dist Span Drop Vel Dist Min Dist Min Sum Clot Trig Dist Min Drop Sec Min Max Span ref ref Vel Sum Shows Clot* Shows Clot* Shows Clot* Shows Clot* meas Parameters ACT Sum Ratio Vel Ratio 0 DistSpan_Ref 0 0 8753 19397 10644 11569    4 0 8763 19419 10656 DropVel_Ref 8 0 8753 19432 10679 9264   13 0 ActBySpan 17 0 534.7 21 1.2 8517 19457 10940 ActByVel 25 2.2 8488 19523 11035 730.3 29 3.3 8461 19483 11022 ActByDistMinSum 34 4.3 8302 19482 11180 521.7 38 5.4 8197 19468 11271 42 6.4 8160 19473 11313 distMinSumRatio 46 7.4 8140 19477 11337   0.24 50 8.5 8117 19461 11344 dropVelRatio 54 9.5 8124 19467 11343   0.91 58 10.6 8142 19462 11320 Target ACT 64 11.6 8110 19478 11368 514   71 0 0.981326 12.6 8090 19447 11357 Closest-Found ACT 74 0 0.999568 13.7 8078 19455 11377 509   78 0 1.00054 14.7 8108 19463 11355 82 0 1.000432 15.8 8090 19465 11375 85 0 1.00367 16.8 8130 19445 11315 88 0 1.004426 17.8 8155 19450 11295 92 0 0.952288 18.9 8077 19451 11374 96 0 0.998057 19.9 8114 19450 11336 99 0 0.746762 21 8087 19454 11367 102 0 0.729598 22 8094 19454 11360 106 0 1.006261 23.1 8073 19419 11346 110 0 0.996762 24.1 8099 19442 11343 113 0 0.810557 25.1 8106 19429 11323 116 0 1.005829 26.2 8087 19443 11356 120 0 1.009607 27.2 8046 19437 11391 124 0 1.007988 28.3 8183 19420 11237 127 0 1.013493 29.3 8036 19439 11403 130 0 1.011766 30.3 8060 19431 11371 134 0 0.996978 31.4 8019 19435 11416 138 0 0.993955 32.4 8040 19429 11389 141 0 1.008528 33.5 8068 19437 11369 144 0 0.746222 34.5 7985 19436 11451 148 0 0.969452 35.5 8098 19444 11346 152 0 1.009931 36.6 7971 19438 11467 155 0 0.963731 37.6 7995 19433 11438 159 0 1.01101 38.7 8060 19434 11374 163 0 1.013925 39.7 8020 19432 11412 167 0 0.972474 40.7 8032 19441 11409 172 0 1.006585 41.8 8056 19415 11359 176 0 0.970207 42.8 7980 19421 11441 182 0 1.010255 43.9 7990 19421 11431 187 0 1.010039 44.9 7986 19418 11432 192 0 0.951101 45.9 7963 19424 11461 198 0 1.001079 47 7991 19448 11457 204 0 1.008744 48 7965 19438 11473 210 0 0.972258 49.1 7960 19427 11467 217 0 1.00367 50.1 8016 19424 11408 224 0 1.005937 51.2 8206 19407 11201 231 0 0.967293 52.2 6937 19398 12461 238 0 0.945272 53.2 7938 19416 11478 246 0 0.9606 54.3 7952 19416 11464 255 0 1.000972 55.3 7907 19415 11508 264 0 0.999784 56.4 7946 19421 11475 273 0 0.961896 57.4 7956 19417 11461 283 0 0.994711 58.4 7972 19380 11408 293 0 0.997841 59.5 8034 19404 11370 304 0 0.984564 60.5 8019 19389 11370 315 0 0.957686 60.5 327 0 0.982837 64 8032 19496 11464 339 0 0.990069 64 352 0 0.981326 67.5 7973 19503 11530 365 0 0.996978 67.5 378 0 0.987263 71 8088 19490 11402 391 0 0.979814 71 11530 9264 404 0 0.980138 71 9091 0 0 0 0 0 NULL 417 0 0.974093 71 430 0 0.968912 74.5 8024 19478 11454 443 0.021263722 0.944193 74.5 11530 9264 456 0.043564699 0.956498 74.5 9260 0 0 0 0 0 NULL 470 0.071224825 0.946244 74.5 482 0.107010113 0.921308 78 7971 19497 11526 496 0.165269254 0.89918 78 11532 9264 509 0.244446365 0.909003 78 9269 0 0 0 0 0 NULL 522 0.342207624 0.872085 78 535 0.452243063 0.871546 81.5 7984 19493 11509 548 0.570057913 0.826209 81.5 11532 9264 561 0.705419656 0.854814 81.5 9268 0 0 0 0 0 NULL 574 0.839830582 0.808398 81.5 587 0.976661769 0.817789 85 7999 19483 11484 600 1.118765667 0.787133 85 9298 0 0 0 0 0 NULL 613 1.262684761 0.784111 85 626 1.406430979 0.752375 88.5 7994 19471 11477 639 1.553894027 0.724849 88.5 9305 0 0 0 0 0 NULL 652 1.704814591 0.675734 88.5 665 1.855302965 0.615609 92 7992 19450 11458 678 2.008384476 0.511766 92 8822 0 0 0 0 0 NULL 691 2.166565822 0.413212 92 704 2.34851759 0.298359 95.5 7960 19483 11523 717 2.633330452 0.211464 95.5 11543 9264 730 3.057394762 0.14864 95.5 9246 0 0 0 0 0 NULL 743 3.663670153 0.087435 95.5 756 4.321808281 0.074806 99 7963 15688 7725 770 5.026795747 0.065091 99 6918 0 0 0 0 0 NULL 782 0.121963869 0.04987 99 796 0.867058518 0.048467 102.5 7977 15630 7653 809 1.630045812 0.047064 102.5 6759 0 0 0 0 0 NULL 822 2.408937678 0.042854 102.5 835 3.193015818 0.03886 106 7971 19491 11520 106 9322 0 0 0 0 0 NULL 106 109.5 7983 19475 11492 109.5 9234 0 0 0 0 0 NULL 109.5 113 7946 16263 8317 113 11543 9264 113 7509 0 0 0 0 0 NULL 113 116.5 7959 19506 11547 116.5 11547 9264 116.5 9318 0 0 0 0 0 NULL 116.5 120 7937 19478 11541 120 11569 9264 120 9353 0 0 0 0 0 NULL 120 123.5 7951 19491 11540 123.5 11569 9264 123.5 9338 0 0 0 0 0 NULL 123.5 127 7951 19497 11546 127 11569 9264 127 9389 0 0 0 0 0 NULL 127 130.5 7971 19484 11513 130.5 9373 0 0 0 0 0 NULL 130.5 134 7995 19486 11491 134 9236 0 0 0 0 0 NULL 134 137.5 7993 19454 11461 137.5 9208 0 0 0 0 0 NULL 137.5 141 7943 19445 11502 141 9343 0 0 0 0 0 NULL 141 144.5 7894 15662 7768 144.5 11569 9264 144.5 6913 0 0 0 0 0 NULL 144.5 148 7978 19451 11473 148 8981 0 0 0 0 0 NULL 148 151.5 7962 19453 11491 151.5 9356 0 0 0 0 0 NULL 151.5 155.2 7988 19452 11464 155.2 8928 0 0 0 0 0 NULL 155.2 159.1 7967 19468 11501 159.1 9366 0 0 0 0 0 NULL 159.1 163.1 7936 19465 11529 163.1 9393 0 0 0 0 0 NULL 163.1 167.4 7978 19447 11469 167.4 9009 0 0 0 0 0 NULL 167.4 171.8 7948 19468 11520 171.8 9325 0 0 0 0 0 NULL 171.8 176.5 7976 19442 11466 176.5 8988 0 0 0 0 0 NULL 176.5 181.5 7956 19476 11520 181.5 9359 0 0 0 0 0 NULL 181.5 186.6 7957 19465 11508 186.6 9357 0 0 0 0 0 NULL 186.6 192 8005 19458 11453 192 8811 0 0 0 0 0 NULL 192 197.7 7966 19457 11491 197.7 9274 0 0 0 0 0 NULL 197.7 203.7 7998 19452 11454 203.7 9345 0 0 0 0 0 NULL 203.7 210 7953 19445 11492 210 9007 0 0 0 0 0 NULL 210 216.6 7961 19454 11493 216.6 9298 0 0 0 0 0 NULL 216.6 223.5 7935 19466 11531 223.5 9319 0 0 0 0 0 NULL 223.5 230.8 7965 19445 11480 230.8 8961 0 0 0 0 0 NULL 230.8 238.4 7957 19447 11490 238.4 8757 0 0 0 0 0 NULL 238.4 246.4 7969 19458 11489 246.4 8899 0 0 0 0 0 NULL 246.4 254.8 7953 19468 11515 254.8 9273 0 0 0 0 0 NULL 254.8 263.7 8046 19464 11418 263.7 9262 0 0 0 0 0 NULL 263.7 272.9 7972 19450 11478 272.9 11569 9264 272.9 8911 0 0 0 0 0 NULL 272.9 282.7 7998 19444 11446 282.7 9215 0 0 0 0 0 NULL 282.7 292.9 7968 19443 11475 292.9 9244 0 0 0 0 0 NULL 292.9 303.6 8037 19459 11422 303.6 9121 0 0 0 0 0 NULL 303.6 314.9 8040 19447 11407 314.9 8872 0 0 0 0 0 NULL 314.9 326.7 8035 19464 11429 326.7 9105 0 0 0 0 0 NULL 326.7 339.1 8039 19456 11417 339.1 9172 0 0 0 0 0 NULL 339.1 352.2 8036 19457 11421 352.2 9091 0 0 0 0 0 NULL 352.2 365.2 8019 19456 11437 365.2 9236 0 0 0 0 0 NULL 365.2 378.2 8034 19467 11433 378.2 9146 0 0 0 0 0 NULL 378.2 391.3 8028 19470 11442 391.3 9077 0 0 0 0 0 NULL 391.3 404.3 7968 19468 11500 404.3 9080 0 0 0 0 0 NULL 404.3 417.4 8032 19458 11426 417.4 9024 0 0 0 0 0 NULL 417.4 430.4 8031 19460 11429 430.4 8976 0 0 0 0 0 NULL 430.4 443.4 8140 19467 11327 443.4 8747 246 0 0 0 0 NULL 443.4 456.5 8152 19471 11319 456.5 8861 504 0 0 0 0 NULL 456.5 469.5 8214 19473 11259 469.5 8766 824 0 0 0 0 NULL 469.5 482.5 8308 19458 11150 482.5 11569 9264 482.5 8535 1238 0 0 0 0 NULL 482.5 495.6 8568 19463 10895 495.6 8330 1912 0 0 0 0 NULL 495.6 508.6 8810 19477 10667 508.6 8421 2828 0 0 0 0 NULL 508.6 521.7 9025 19450 10425 521.7 8079 3959 0 0 0 1 NULL 521.7 534.7 9167 19449 10282 534.7 8074 5232 1 0 0 2 NULL 534.7 547.7 9257 19449 10192 547.7 7654 6595 2 0 0 3 DIST_MIN_SUM 547.8 547.8 547.8 547.8 560.8 9460 19476 10016 560.8 7919 8161 3 0 0 4 DIST_SPAN 560.8 573.8 9449 19455 10006 573.8 7489 9716 4 0 0 5 DIST_SPAN 573.8 586.9 9477 19493 10016 586.9 7576 11299 5 0 0 6 DIST_SPAN 586.9 599.9 9538 19461 9923 599.9 7292 12943 6 0 0 7 DIST_SPAN 599.9 613 9559 19499 9940 613 7264 14608 7 0 0 8 DIST_SPAN 613 626 9557 19508 9951 626 6970 16271 8 0 0 9 DIST_SPAN 626 639 9600 19490 9890 639 6715 17977 9 0 0 10 DIST_SPAN 639 652.1 9640 19503 9863 652.1 6260 19723 10 0 0 11 DIST_SPAN 652.1 665.1 9635 19509 9874 665.1 5703 21464 11 0 0 12 DIST_SPAN 665.1 678.2 9665 19479 9814 678.2 4741 23235 12 0 0 13 DIST_SPAN 678.2 691.2 9724 19493 9769 691.2 3828 25065 13 0 0 14 DIST_SPAN 691.2 704.2 9999 19498 9499 704.2 2764 27170 14 0 0 15 DIST_SPAN 704.2 717.3 11189 19495 8306 717.3 1959 30465 15 0 0 16 DIST_SPAN 717.3 730.3 12800 19476 6676 730.3 1377 35371 16 1 0 17 DIST_SPAN 730.3 743.4 14908 19470 4562 743.4 810 42385 17 2 0 18 DIST_SPAN 743.4 756.4 15508 19480 3972 756.4 693 49999 18 3 0 19 DIST_SPAN 756.4 769.5 16050 19444 3394 769.5 603 58155 19 4 0 20 DIST_SPAN 769.5 782.5 16686 19448 2762 782.5 462 1411 20 5 0 0 DIST_SPAN 782.5 795.5 16514 19440 2926 795.5 449 10031 21 6 0 1 DIST_SPAN 795.5 808.6 16721 19456 2735 808.6 436 18858 22 7 0 2 DIST_SPAN 808.6 821.6 16905 19462 2557 821.6 397 27869 23 8 0 3 DIST_SPAN 821.6 834.7 16965 19445 2480 834.7 360 36940 24 9 0 4 DIST_SPAN 834.7 

What is claimed is:
 1. A method of detecting the formation of a clot in a fluid sample during a coagulation test phase including one or more test periods, the method comprising: a. providing a test chamber having a top and a bottom and further providing a disk positioned within the test chamber; b. filling the test chamber with the fluid sample; c. conducting a plurality of test cycles, each test cycle including: i. positioning the disk at a disk maximum position within the test chamber; wherein the disk maximum position is the highest point at which the disk is positioned during the respective test cycle; ii. dropping the disk; iii. determining a highest disk maximum position which is the highest disk maximum position measured during all of the test cycles conducted; and iv. determining a current disk minimal position which is the lowest position at which the disk falls within the test chamber during the last test cycle and a lowest disk minimal position which is the lowest disk minimal position measured during all of the test cycles conducted; d. calculating a reference disk-span being equal to the highest disk maximum position minus a lowest disk minimal position; e. identifying a reference for enabling disk minimum position being equal to the lowest disk minimal position; f. calculating a reference for enabling integration of disk minimum position equaling the reference disk minimum position+(Y %×the reference disk-span); wherein Y % is a value between 0 and 100%; g. subtracting the lowest disk minimal position from the current disk minimal position to calculate a change in minimal position; h. comparing the change in minimal position to the reference for enabling integration of disk minimum position; wherein, if the change in minimal position is less than the reference for enabling integration of disk minimum position, a clot will not be indicated to be detected and when the change in minimal position is greater than the reference for enabling integration of disk minimum position, then a disk change value is set to be the change in minimal position; i. adding each disk change value of all conducted test cycles to calculate a distance minimum sum; and j. during at least one specified test period, comparing the distance minimum sum to a clot detection reference; wherein if the distance minimum sum is greater than the clot detection reference, a clot is indicated to be detected; wherein if the distance minimum sum is not greater than the clot detection reference, a clot is not indicated to be detected.
 2. The method of claim 1, further comprising the step of measuring a first parameter during each test cycle; wherein the first parameter is indicative of a viscosity of the fluid sample.
 3. The method of claim 2, further comprising the step of assessing the first parameter either indicating a clot to be detected or not indicating a clot to be detected independent of step (j).
 4. The method of claim 3, further comprising the step of measuring a second parameter during each test cycle; wherein the second parameter is indicative of a viscosity of the fluid sample.
 5. The method of claim 4, further comprising the step of assessing the second parameter and the first parameter and either indicating a clot to be detected or not indicating a clot to be detected independent of step (j).
 6. The method of claim 1, wherein each test cycle is conducted in an equal amount of time.
 7. The method of claim 1, wherein the disk is made of a ferromagnetic material.
 8. The method of claim 1, wherein a height of the test chamber is divided into a plurality of lift zones; wherein during step (c)(i) the disk is positioned with a magnetic field and the magnetic field varies depending on the lift zone in which the disk originates.
 9. The method of claim 1, wherein the clot detection reference varies as the repeated test cycles are conducted.
 10. The method of claim 1, wherein the fluid sample includes heparin.
 11. The method of claim 1, wherein the fluid sample includes a viscosity-altering substance and the method further comprising a sample mix phase prior to step (c).
 12. The method of claim 1, wherein the clot detection reference is set to equal a clot detection threshold x the Reference Disk-Span.
 13. The method of claim 12, wherein the clot detection threshold changes over time.
 14. The method of claim 1, wherein Y % is 2%.
 15. A method of detecting the formation of a clot in a fluid sample during a coagulation test phase including one or more test periods, the method comprising: a. providing a test chamber having a top and a bottom and further providing a disk positioned within the test chamber; b. filling the test chamber with the fluid sample; c. conducting a first test cycle including: i. positioning the disk at a first disk maximum position within the test chamber; wherein the first disk maximum position is the highest point at which the disk is positioned during the first test cycle; ii. measuring the first disk maximum position; iii. dropping the disk; and iv. determining a first disk minimal position which is the lowest point at which the disk falls within the test chamber during the first test cycle; d. conducting a second test cycle including: i. positioning the disk at a second disk maximum position within the test chamber; wherein the second disk maximum position is the highest point at which the disk is positioned during the second test cycle; ii. measuring the second disk maximum position; iii. dropping the disk; and iv. determining a second disk minimal position which is the lowest point at which the disk falls within the test chamber during the second test cycle; e. conducting a third test cycle including: i. positioning the disk at a third disk maximum position within the test chamber; wherein the third disk maximum position is the highest point at which the disk is positioned during the third test cycle; ii. measuring the third disk maximum position; iii. dropping the disk; and iv. determining a third disk minimal position which is the lowest point at which the disk falls within the test chamber during the third test cycle; f. calculating a reference disk-span being equal to the highest of the first, second and third disk maximum positions minus the lowest of the first, second and third disk minimal positions; g. identifying a reference disk minimum position being equal to the lowest of the first, second and third disk minimal positions; h. calculating a clot detection reference being equal to the reference disk minimum position+(X %×the Reference Disk-Span); wherein X % is a value between 0 and 100%; i. conducting a fourth test cycle including: i. positioning the disk at a fourth disk maximum position within the test chamber; wherein the fourth disk maximum position is the highest point at which the disk is positioned during the fourth test cycle; ii. measuring the fourth disk maximum position; iii. dropping the disk; and iv. determining a fourth disk minimal position which is the lowest point at which the disk falls within the test chamber during the fourth test cycle; and j. comparing the fourth disk minimal position to the clot detection reference; and k. repeating steps j(i-iv) to conduct fifth and sixth test cycles and comparing the fifth and sixth disk minimum positions to the clot detection reference; and l. either declaring a clot to be detected when all of the fourth-sixth disk minimum positions are greater than the clot detection reference or not indicating a clot to be detected when any of the fourth-sixth disk minimum positions are not greater than the clot detection reference.
 16. The method of claim 15, further comprising the step of measuring a first parameter during step (i)(ii); wherein the first parameter is indicative of a viscosity of the fluid sample.
 17. The method of claim 16, further comprising the step of assessing a change in the first parameter and either indicating a clot to be detected or not indicating a clot to be detected independent of step (l).
 18. The method of claim 15, wherein, after step (j), the method further comprises the steps of updating each of: 1) the reference disk-span being equal to the highest of the first-fourth disk maximum positions minus the lowest of the first, second, third, and fourth disk minimum positions; 2) the reference disk minimum position to equal the lowest of the first, second, third and fourth disk minimum positions; and 3) the clot detection reference.
 19. The method of claim 15, wherein X % is greater than 8%.
 20. The method of claim 15, wherein X % varies throughout the coagulation test phase. 